The present invention relates to method and apparatus for adjusting die stroke, and more particularly to die stroke adjusting method and apparatus in which adjustable helical springs equipped with displacement sensors and rotation sleeve drivers are employed to accurately adjust a die stroke under control of a central processing unit.
In a conventional molding technology, molten material is poured from a melting furnace into a cavity of a bottom die and a downward force is applied on a top die against the bottom die, so that a molded product is formed. In the process of molding, there are many factors, including the arrangement of dies, the pouring of molding material, the control of mold temperature, the control of die stroke and travel time, the process of conservative pressure, etc., that have influences on the final shape, the surface smoothness, and the wall thickness of the molded product. In other words, an accumulative error could result from overall parameters in the process of molding. However, such change in the accuracy of products is usually detected only when a considerable quantity of inferior products have been produced. At this point, the production has to be interrupted to examine the production equipment, to replace dies and/or accessories, etc. A lot of time and efforts would be required to do so and it is possible that the problem is not found or overcome.
Moreover, in the conventional variable-volume mold-filling process, there might be more than one size for the same type of product to provide consumers with more choices. To reduce the times of replacing dies or to reduce the replacement of stroke control apparatus in order to increase the yield, it is a common practice to use a variable-volume mold cavity in a part of or the whole space of the same one mold cavity in order to change the specifications of products. When an amount of plastic material is injected into a variable-volume mold cavity, any difference in the injection pressure and any displacement of the movable die would have influences on the specifications and surface smoothness of the resultant products. It is therefore necessary to precisely control any change of the pressure of the molten plastic material in the variable-volume mold cavity against each point on the movable die and any resultant displacement of the movable die in order to meet the required high accuracy of the products.
In brief, the conventional molding skill and the conventional variable-volume mold-filling skill all need improvements to overcome the above-mentioned problems and to produce perfect products.
A primary object of the present invention is to provide an apparatus for adjusting die stroke so as to reduce errors of a molded product.
Another object of the present invention is to provide a method for adjusting die stroke so as to replace the conventional empirical method in determining problems in a molding process, and to effectively reduce the rate of bad yield of molded products and accordingly the manufacturing cost thereof.
To achieve the above and other objects, the apparatus for adjusting die stroke of the present invention mainly includes a plurality of adjustable helical springs, each of which is equipped with a displacement sensor, a rotation sleeve, and a rotation sleeve driver, a plurality of supporting rods, and a central processing unit. The displacement sensors send signals of magnitude of deformation of the adjustable helical springs to the central processing unit for comparing with errors measured at different points of a molded product released from the dies. Based on the comparison results, the central processing unit sends adjusting signals to the rotation sleeve drivers for the same to turn the rotation sleeves and thereby adjusts the helical springs to a required modulus of elasticity for use in a next cycle of molding process.
It is known that when the adjustable helical spring is under a load, an increased modulus of elasticity allows the spring to have a reduced magnitude of deformation, and a reduced modulus of elasticity allows the spring to have an increased magnitude of deformation. When this principle is applied to the molding process having a constant force applied by an oil-pressure cylinder on the molding dies, the adjustable helical springs of the apparatus of the present invention could be adjusted from time to time to reduce errors in an entire stroke of the top die. And when the same principle is applied to the variable-volume mold-filling process having a constant injection pressure in subsequent injection process, the adjustable helical springs of the apparatus of the present invention could be adjusted from time to time to adjust the displacement of the entire movable die.
The apparatus for adjusting die stroke is mounted between an oil-pressure cylinder and a top die movable above a bottom die in the case of a molding process, and between a plate of top die and a movable die in the case of a variable-volume mold-filling process. The apparatus includes an upper stroke limiting plate, a lower stroke limiting plate, a plurality of supporting rods, a plurality of adjustable helical springs, and a central processing unit.
The upper stroke limiting plate is associated with a pressing plate of the oil-pressure cylinder in the case of molding process, or with the plate of top die in the case of variable-volume mold-filling process, and is provided at a bottom surface with a plurality of adjustable spring seats and a plurality of adjustable supporting rod seats.
The lower stroke limiting plate is associated with a pressing plate of the top die in the case of molding process, or with the movable die in the case of variable-volume mold-filling process, and is provided at a top surface with a plurality of fixed spring seat and a plurality of fixed supporting rod seats corresponding to the adjustable spring seats and the adjustable supporting rod seats, respectively.
Each of the supporting rods is mounted between a pair of adjustable supporting rod seat and fixed supporting rod seat for adjusting an initial distance between the upper and the lower stroke limiting plates and for supporting an initial load set for the apparatus. The purpose of setting the initial load is to effectively reduce errors in a whole stroke of the top die at a final stage of the molding process, and to overcome a total mold-filling pressure at a first stage of the variable-volume mold-filling process in order to keep the movable die from undesired displacement.
Each of the adjustable helical springs is mounted between a pair of adjustable spring seat and fixed spring seat, and includes a male case, a female case, a rotation sleeve rotatably mounted between the male and the female cases, and a helical spring enclosed in and axially extended between the male and the female cases. A displacement sensor is connected to each adjustable helical spring for detecting a change in length of the helical spring and sending a signal of the detected result to the central processing unit. The rotation sleeve is associated with a rotation sleeve driver that receives an adjusting signal output by the central processing unit to drive the rotation sleeve in order to obtain a required modulus of elasticity for the helical spring. When the helical springs are subject to the initial force and deform, their screw pitches change, too. By selecting male cases and rotation sleeves having proper screw pitches that are the same as that of the helical springs under the initial force, and adjusting the adjustable spring seats and the supporting rods on the apparatus to adjust the lengths of the adjustable helical springs, the helical springs maybe adjusted to a required initial force. By adjusting the supporting rods and the adjustable supporting rod seats, an overall height of the apparatus could be adjusted. And, by adjusting the adjustable spring seats, the initial force of the adjustable helical springs could be separately adjusted.
The central processing unit sets a load and a magnitude of deformation for each adjustable helical spring based on a total applied force in the molding process and the variable-volume mold-filling process and positions of the adjustable helical springs relative to the molding dies, and receives from the displacement sensors an actual magnitude of deformation of the adjustable helical springs under a load and obtains errors of a molded product, so as to modify the preset load and magnitude of deformation for each adjustable helical spring. The central processing unit also compares the modified settings of load and magnitude of deformation of the adjustable helical springs with basic parameters set for the adjustable helical springs and outputs adjusting signals to respective rotation sleeve drivers, so that each adjustable helical spring could have the required modulus of elasticity for use in a next cycle of the molding process and the variable-volume mold-filling process.
Since the apparatus for adjusting die stroke may have several adjustable helical springs having identical or different specifications and there is an error in each helical spring, even helical springs having the same specifications do not necessarily have the same modulus of elasticity, and the rotation sleeves do not engage with coils of the helical springs at the same positions. For helical springs having the same load to have different magnitudes of deformation, or for helical springs having different loads to have the same magnitude of deformation, the central processing unit has to store basic parameters for each adjustable helical spring before the apparatus for adjusting die stroke is started to operate.
These basic parameters for each adjustable helical spring include an angle by which the rotation sleeve driver rotates, a load of the helical spring, and a magnitude of deformation of the helical spring. For the central processing unit to conduct operations and modification of settings when the apparatus operates, the basic parameters form a parameter table of three-dimensional matrix. When the rotation sleeve of each adjustable helical spring is driven to rotate an angle, the modulus of elasticity of the adjustable helical spring is changed. Thus, several fixed applied forces used to cause corresponding deformation of a helical spring constitute a parameter table of two-dimensional matrix for the modulus of elasticity. Or, a fixed applied force and several rotating angles of the rotation sleeves used to cause corresponding deformation of several helical springs constitute a parameter table of two-dimensional matrix for the applied force. The applied force could be obtained from a tension/pressure machine, and the magnitude of deformation could be obtained from the displacement sensors associated with the adjustable helical springs. Since the basic parameters of the adjustable helical springs only define a limited rotating angle for the rotation sleeve driver, a calculated modulus of elasticity from the central processing unit in an actual operation of the apparatus might not be included in the basic parameters. However, the central processing unit may also obtain a rotating angle for the rotation sleeve driver based on the existing basic parameters through an interpolation.
Since screw pitches of the rotation sleeve and the male case of each adjustable helical spring are the same as that of the helical spring are subject to the initial force, the rotation sleeve driver could function only when the apparatus for adjusting die stroke is not under any load. That is, in the molding process or the variable-volume mold-filling process, the rotation sleeve drivers could be actuated to adjust the adjustable helical springs only when the mold product has been released from the molding dies.
The present invention provides a cyclic adjusting mode in an attempt to form the best products with molding dies within a lowest possible number of process cycles through the convergence method. If the central processing unit could automatically read the errors of the molded product to adjust any accumulative error occurred in the molding process and the variable-volume mold-filling process from time to time, the rate of bad yield of the molded products could be minimized to largely facilitate the control and improvement of a molding process.